The present invention relates to a light panel, comprising a light source and a panel element, said panel element being manufactured from a substantially transparent material for transmitting light thereby. The panel element is configured as a waveguide panel, inside which the light beams propagate with total reflection and get outcoupled therefrom with a diffractive outcoupling system.
Diffractive structures refer in optics to all fine structures of a surface, which condition the passage of light on the basis of the diffraction effect. Thus, the details of fine structures must be in the same order of magnitude as the wavelength of light, even smaller than that. Most prior known microprismatic structures are not even diffractive structures as conditioning the passage of a beam therein is based on the refraction effect. On the other hand, the hologram is not a grating, whereas the grid does not produce a three-dimensional image or light. The local grid, in turn, refers to a local grating unit, such as e.g. a pixel. Furthermore, the entire grating structure may be constituted by a great variety of miscellaneous grating units.
It is prior known to outfit e.g. illuminators and indicator panels in exit ways with conventional incandescent lamps or fluorescent tubes. One such example can be found e.g. in Finnish utility model No. 1533. The cited solution comprises a light panel fitted with an illuminator cover, wherein the light of a fluorescent illuminator tube fitted inside the illuminator cover is directed out by way of the perimeter of a panel element mounted in connection with a light source. In this particular solution, the illuminator cover is provided with an elongated, cover-length opening for replacing the fluorescent illuminator tube therethrough from above. However, a drawback with this type of traditional indicator panels is the short service life of incandescent lamps and fluorescent tubes as the exit lights must be switched on all the time.
On the other hand, especially for the illumination of mobile phone displays, it is prior knowledge to use diffractive structures for the light outcoupling from waveguides. Refractive microprismatic or the like structures have also been developed for this purpose. However, a weakness with these are bright lines produced by the edges of prisms, which are difficult to eliminate in order to provide uniform lighting. Neither are the outcoupling capacities of prism structures equal to those of grating structures. In reference to actual diffractive solutions, one notable example is U.S. Pat. No. 5,703,667, which discloses a display lighting for use as a waveguide. The waveguide comprises a transparent panel, having its bottom surface provided with a diffractive grating structure for re-directing light that has been delivered in at the perimeter of the panel. The grating structure is designed in such a way that the surface area of a grating structure present in a unit area has a variable ratio to the gratingless surface area present therein. Thus, the grating is not plotted all over the waveguide. In this solution, it is possible to equalize the intensity of light outcoupling by making less grating structure close to a light source than far away from the light source. Subsequently, especially with large-size panels, the result is likely to be that the grating area will be so sparse that it begins to show in the outcoupling, whereby the uniformity is lost. The cited invention is also limited to planar structures which always re-direct light from the rear surface. The weakness of all prior known structures is more or less non-uniform lighting, a planar structure, a non-optimally designed grating pattern, and a very poor incoupling capacity.
The light panel of this invention has an object of providing a decisive improvement over the above problems and, in doing so, to raise essentially the available state of the art. In order to achieve this objective, a light panel of the invention is principally characterized in that an outcoupling system, such as a grating structure or the like, is arranged on the entire panel element all over its light surface, such that divergent recesses and/or grooves of various sizes and/or shapes are used to constitute divergent local gratings of various sizes and/or shapes, such as multi-shaped and/or binary pixels and/or units, having the filling factor, shape, profile and/or size thereof optimized in such a way that the diffraction efficiency is a function of place.
The most important benefits gained by a light panel of the invention include its simplicity, efficiency, and reliability in operation, since, in this conjunction, it is first of all possible to make use of very low-power leds as a light source. On the other hand, by virtue of a total-reflection based waveguide panel construction utilized in the invention, the light source can be optimized in all aspects since it is possible to minimize unintentional reflection losses and other light losses. By virtue of a principle exploited in the invention, it is further possible to make extremely thin structures, which can be embedded in a substrate, or else to manufacture flexible or preformed structures by providing every time such conditions that the limit or threshold angle of total reflection is not exceeded in the panel element. The invention makes it further possible to design the panel element for example as a box-type structure, such as a quadratic or tubular xe2x80x9clamp postxe2x80x9d. In addition, it is also possible to operate a light panel of the invention in such a way that it is activable in one or more sections for different colours, e.g. by using one or more variable-colour or multicolour LEDS, or e.g. by changing the intensity/operating voltage of a light source, etc.